Low energy reclosing pulse test

ABSTRACT

A method for performing a low energy pulse testing in a power distribution network that causes contacts to close and then open in about one fundamental frequency cycle of current flow time and close on a voltage waveform that produces symmetrical fault current. The method includes energizing a magnetic actuator to move the actuator against the bias of a spring to move a movable contact towards a fixed contact. The method also includes de-energizing the actuator when the movable contact makes contact with the fixed contact so as to allow the spring to move the movable contact away from the fixed contact so that the amount of time that the current conducts is about one fundamental frequency cycle of the current, where energizing the magnetic actuator occurs when an applied voltage on the switch assembly is at a peak of the voltage wave so that the current is symmetric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is continuation of prior U.S. Pat. No. 11,328,885issued on May 10, 2022, which claims the benefit of priority from theU.S. Provisional Application No. 62/944,296, filed on Dec. 5, 2019, thedisclosures of which are hereby expressly incorporated herein byreference for all purposes.

BACKGROUND Field

The present disclosure relates generally to a system and method forperforming a low energy pulse testing operation in a power distributionnetwork to determine if a fault condition is present.

Discussion of the Related Art

An electrical power distribution network, often referred to as anelectrical grid, typically includes a number of power generation plantseach having a number of power generators, such as gas turbines, nuclearreactors, coal-fired generators, hydro-electric dams, etc. The powerplants provide power at a variety of medium voltages that are thenstepped up by transformers to a high voltage AC signal to be connectedto high voltage transmission lines that deliver electrical power to anumber of substations typically located within a community, where thevoltage is stepped down by transformers to a medium voltage fordistribution. The substations provide the medium voltage power to anumber of three-phase feeders including three single-phase feeder linesthat provide medium voltage to various distribution transformers andlateral line connections. A number of three-phase and single-phaselateral lines are tapped off of the feeder that provide the mediumvoltage to various distribution transformers, where the voltage isstepped down to a low voltage and is provided to a number of loads, suchas homes, businesses, etc.

Power distribution networks of the type referred to above typicallyinclude a number of switching devices, breakers, reclosers,interrupters, etc. that control the flow of power throughout thenetwork. A vacuum interrupter is a switch that has particularapplication for many of these types of devices. A vacuum interrupteremploys opposing contacts, one fixed and one movable, positioned withina vacuum enclosure. When the interrupter is opened by moving the movablecontact away from the fixed contact the arc that is created between thecontacts is quickly extinguished as the AC current goes through zero inthe vacuum. A vapor shield is typically provided around the contacts tocontain the by-products of the arcing. For certain applications, thevacuum interrupter is encapsulated in a solid insulation housing thatmay have a grounded external surface.

Periodically, faults occur in the distribution network as a result ofvarious things, such as animals touching the lines, lightning strikes,tree branches falling on the lines, vehicle collisions with utilitypoles, etc. Faults may create a short-circuit that increases the stresson the network, which may cause the current flow from the substation tosignificantly increase, for example, many times above the normalcurrent, along the fault path. This amount of current causes theelectrical lines to significantly heat up and possibly melt, and alsocould cause mechanical damage to various components in the substationand in the network. These faults are many times transient orintermittent faults as opposed to a persistent or bolted fault, wherethe thing that caused the fault is removed a short time after the faultoccurs, for example, a lightning strike. In such cases, the distributionnetwork will almost immediately begin operating normally after a briefdisconnection from the source of power.

Fault interrupters, for example, reclosers that employ vacuuminterrupters, are provided on utility poles and in underground circuitsalong a power line and have a switch to allow or prevent power flowdownstream of the recloser. These reclosers detect the current andvoltage on the line to monitor current flow and have controls thatindicate problems with the network circuit, such as detecting a highcurrent fault event. If such a high fault current is detected therecloser is opened in response thereto, and then after a short delayclosed to determine whether the fault is a transient fault. If a highfault current flows when the recloser is closed after opening, it isimmediately re-opened. If the fault current is detected a second time,or multiple times, during subsequent opening and closing operationsindicating a persistent fault, then the recloser remains open, where thetime between detection tests may increase after each test. For a typicalreclosing operation for fault detection tests, about 3-6 cycles or 50 to100 ms of fault current pass through the recloser before it is opened,but testing on delayed curves can allow fault current to flow for muchlonger times.

When a fault is detected, it is desirable that the first faultinterrupter upstream from the fault be opened as soon as possible sothat the fault is quickly removed from the network so that the loadsupstream of that fault interrupter are not disconnected from the powersource and service is not interrupted to them. It is further desirablethat if the first fault interrupter upstream from the fault does notopen for whatever reason, then a next fault interrupter upstream fromthe fault is opened, and so on. In order to accomplish this, it isnecessary that some type of communications or coordination protectionscheme be employed in the network so that the desired fault interrupteris opened in response to the fault.

During the traditional reclosing operation discussed above, the vacuuminterrupter contacts in the recloser are closed without regard to adesired phase angle. This results in a random closing angle that oftencreates an asymmetrical fault current, where the current cycle is offsetfrom zero, i.e., has high magnitude peaks in one polarity and lowerpeaks in the reverse polarity relative to zero. The high magnitude faultcurrent peaks, depending on the length of time they are occurring,causes significant forces and stresses on the components in the networkthat may reduce their life. For the traditional reclosing operationhaving current flow times over 3-6 cycles and longer times for delayedcurve operation, these forces and stresses can be considerable. Whenconsidering the life of a transformer winding, one cause of end of lifecan be fatigue in the winding, which is the accumulation of highmechanical and thermal stress cycles. Stress is the result of thecurrent in the winding, where higher current results in higher stress.Doubling the stress that can cause fatigue from the asymmetrical faultcurrents described above can result in a tenfold or more reduction infatigue life, i.e., the life before fatigue causes cracking. This stresscan be reduced by reducing the peak current and by reducing the numberof stress cycles.

In order to overcome this problem, reclosers have been developed in theart that use pulse testing technologies where the closing and thenopening of the vacuum interrupter contacts is performed in a pulsedmanner so that the full fundamental frequency multiple cycle faultcurrent is not applied to the network while the recloser is testing todetermine if the fault is still present. Typically these pulses areabout one-half of a fundamental frequency current cycle. Additionally,these reclosers close at the appropriate point on the voltage waveformto eliminate the asymmetrical current, which reduces the stresses due tohigh current in the components.

Pulse closing technologies have been successful in significantlyreducing fault current stresses on network equipment during reclosertesting. However, the switching devices required to generate these shortpulse durations are relatively complicated and expensive. For example,vacuum interrupters employed to generate these pulses often use twomagnetic actuators, one to close the contacts and one to quickly openthe contacts using the moving mass of the opening actuator to reversethe direction of the closing actuator, well understood by those skilledin the art.

SUMMARY

The following discussion discloses and describes a system and method forperforming a low energy pulse testing operation in a power distributionnetwork that causes recloser contacts to close and then open in such away that produces current flow for one fundamental frequency cycle afterclosing on a voltage waveform that produces symmetrical current. Themethod includes energizing a magnetic actuator to move the movablecontact towards the fixed contact, where AC current conducts across agap between the movable contact and the fixed contact before the movablecontact and the fixed contact make contact. The actuator movement toclose the contacts pushes against the bias of at least one openingspring coupled to the movable contact. A compliance spring coupled tothe movable contact with some preload is compressed further as the twocontacts touch. The method also includes de-energizing the magneticactuator or reversing the voltage on the magnetic actuator when themovable contact makes contact with the fixed contact so as to allow thebias of the opening and compliance springs to first compress absorbingenergy from the motion of the moving mass, then to expand moving themovable contact away from the fixed contact so that the amount of timethat the current conducts between the movable contact and the fixedcontact is about one fundamental frequency cycle, and where energizingthe magnetic actuator occurs at a time at or near a peak of the voltagewave so that the current through the switch assembly is symmetric.

Additional features of the disclosure will become apparent from thefollowing description and appended claims, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic illustration of an electrical powerdistribution network;

FIG. 2 is a side, cross-sectional type view of a magnetic actuatorswitch assembly in an open position that can be used in a recloser inthe power distribution network shown in FIG. 1 ;

FIG. 3 is a side, cross-sectional type view of the magnetic actuatorswitch assembly shown in FIG. 2 in a closed position;

FIG. 4 is a graph with time on the horizontal axis and magnitude on thevertical axis showing a relationship between symmetrical andasymmetrical current relative to voltage angle; and

FIG. 5 is a graph with time on the horizontal axis and actuator housingposition on the vertical axis showing position versus time of theactuator housing in the switch assembly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the disclosure directedto a system and method for performing a low energy fault pulse testingoperation in a power distribution network that causes recloser contactsto close and then open in approximately one fundamental frequency cycleof current flow time and close on a voltage waveform that producessymmetrical fault current is merely exemplary in nature, and is in noway intended to limit the invention or its applications or uses.

The present disclosure proposes a system and method that replaces theknown fault pulse testing process in a power distribution network with alow energy fault pulse testing process, which results in lower costswitching devices. The method includes controlling the position of theswitch contacts in a recloser so that they conduct for a short timeduration that limits the current conduction time to one fundamentalfrequency cycle. The method also includes closing the switch contacts ata point on the voltage waveform that results in the flow of symmetricalcurrent instead of asymmetrical current, which is accomplished byrecognizing that asymmetrical currents occur from closing the contactsat a certain voltage angle, where the preferred angle for asymmetricalcurrent is at or near the peak of the voltage waveform. The disclosedlow energy testing process is distinguished from the conventionalrecloser random closing operation since the recloser protectionfunctions perform their normal fault detection processes, therebyextending the potential fault duration to several power system cycles ora much longer time.

FIG. 1 is a schematic type diagram of an electrical power distributionnetwork 10 including an electrical substation 12 that steps down highvoltage power from a high voltage power line (not shown) to mediumvoltage power, a three-phase feeder 14 that receives medium voltagepower from the substation 12, and a lateral line 16 that receives themedium voltage power from the feeder 14. The medium voltage is steppeddown to a low voltage by a number of distribution transformers 18strategically positioned along the lateral line 16, and the low voltageis then provided through a secondary service conductor 38 to a number ofloads 20 represented here as homes. The lateral line 16 includes a fuse28 positioned between the feeder 14 and the first load 20 on the lateralline 16 proximate to a tap location where the lateral line 16 isconnected to the feeder 14. The fuse 28 is an independent electricaldevice that is not in communication with other components or devices inthe network 10, where the fuse 28 creates an open circuit if an elementwithin the fuse 28 heats up above a predetermined temperature as aresult of high fault current so as to prevent short-circuit faults onthe lateral line 16 from affecting other parts of the network 10.

The network 10 includes a number of reclosers of the type referred toabove provided at certain intervals along the feeder 14 represented byreclosers 24 and 26 that receive the medium voltage from the substation12 on the feeder 14. Although only shown as a single line, the feeder 14would include three lines, one for each phase, where a three-phase orthree separate reclosers would be provided in each line. A number ofutility poles 22 are provided along the feeder 14 and the lateral line16, where the recloser 24 would be mounted on certain ones of the poles22. The recloser 24 includes a vacuum interrupter switch or otherswitching device 30 for opening and closing the recloser 24 to allow orprevent current flow therethrough on the feeder 14, where the switch 30is capable of providing pulses for pulse testing consistent with thediscussion herein. The recloser 24 also includes sensors 32 formeasuring the current and voltage of the power signal propagating on thefeeder 14, an electronic controller 34 for processing the measurementsignals and controlling the position of the switch 30, and an optionaltransceiver 36 for transmitting data and messages to a control facilityand/or to other reclosers and components in the system 10. Theconfiguration and operation of reclosers and switching devices of thistype are well understood by those skilled in the art.

FIG. 2 is a side, cross-sectional type view of a magnetic actuatorswitch assembly 50 in an open position and FIG. 3 is a side,cross-sectional type view of the switch assembly 50 in a closedposition, where the switch assembly 50 can be used in the switch 30. Theswitch assembly 50 includes a fixed contact 52 and a movable contact 54having a defined mass, for example, 0.4 kg, that would be positioned in,for example, a vacuum bottle of a vacuum interrupter, where the contacts52 and 54 are shown spaced apart from each other across a vacuum gap 56in the open position, and where the distance of the gap 56 is determinedso as to prevent conduction between the contacts 52 and 54 in the openposition based on the voltages employed in the network 10. The switchassembly 50 further includes an actuator 58 having an actuator housing60 with a wide housing portion 62 and a narrow housing portion 64. Anopen spring 66 is wound around the narrow housing portion 64 and ispositioned against the wide housing portion 62 and a conductivestructure 68, where the current path on the power line flows through acurrent transfer coupling 70 coupled to the structure 68 and the movablecontact 54. A flange 72 attached to the movable contact 54 opposite fromthe gap 56 is positioned within the narrow housing portion 64 andengages a flange 74 at an end of the narrow housing portion 64 oppositeto the wide housing portion 62. A compliance spring 78 is positioned inthe narrow housing portion 64 against the flange 72 and a wall 80, wherethe spring 78 has, in one non-limiting embodiment, a 266 Newton preloadand a 334 Newton full deflection. The actuator 58 further includes asolenoid 84 positioned within the wide housing portion 62 and includinga core 86, a coil 88 wrapped around a center portion 90 of the core 86and movable core 92 attached to the housing 60, where a gap 102 isprovided between the movable core 92 and the core 86 when the contacts52 and 54 are open. The core 86 is an E-shaped core in this non-limitingembodiment, where other shaped cores may be applicable such as round potcores. A plunger 94 is secured to a fixed member 96 by a spring 98 andhaving a coil 100 wrapped around it.

To close the contacts 52 and 54, the coil 88 is energized so thatmagnetic flux across the gap 102 between the magnetic elements draws themovable core 92 towards the E-shaped core 86, which moves the housing 60against the bias of the open spring 66 and causes the compliance spring78 to push the movable contact 54 against the fixed contact 52, wherethe bias of the springs 66 and 78 hold the contacts 52 and 54 togetherin a tight engagement. The coil 100 is de-energized which causes thespring 98 to move the plunger 94 upwards and hold the actuator 58 in theclosed position. To open the contacts 52 and 54, the coil 100 isenergized to pull the plunger 94 downward against the friction of themoving part of the actuator 58 and the bias of the spring 98 so that theopen spring 66 and the compliance spring 78 push the housing 60 to theleft and moves the movable core 92 away from the E-shaped core 86. Sinceit is necessary to quickly open the contacts 52 and 54 when faultcurrent is detected, the spring forces used to move the contact 54 awayfrom the contact 52 are relatively high. Additionally, it is desirableto coordinate the opening of the contacts 52 and 54 with other reclosersso that those reclosers closest to the fault are opened first, whichrequires a force to be applied to the movable contact 54 to hold thecontacts 52 and 54 closed for some period of time when a fault isdetected to coordinate with faster reclosers.

As mentioned above, this disclosure describes a low energy fault pulsetesting process that causes about one fundamental frequency cycle ofsymmetrical current during each pulse test. Process algorithms controlthe switch assembly 50 to provide point-on-wave closing of the contacts52 and 54 to obtain the short duration symmetric current flow thatincludes controlling the relative position of the vacuum interruptercontacts 52 and 54 to provide the desired time to start and end currentconduction across the contacts 52 and 54 by controlling the time whenthe actuator 58 begins moving to close the contacts 52 and 54 andcontrolling when the coil 88 is turned off. FIGS. 4 and 5 are graphs tohelp illustrate the control of the switch assembly 50 in this manner.

FIG. 4 is a graph with time on the horizontal axis and magnitude on thevertical axis showing a relationship between symmetrical andasymmetrical current relative to a voltage waveform. Graph line 110 isthe measured voltage at the switch assembly 50 during the fault andshows the zero cross-overs of the voltage signal. Graph line 112 showsthe measured fault current at the switch assembly 50 if the contacts 52and 54 begin conduction at a zero cross-over of the voltage, and showsthe current being offset or asymmetrical where the positive peaks aremuch higher in absolute magnitude than the negative peaks, which leadsto significant stress on the electrical components in the network 10that are subjected to the fault current because of the high currentmagnitude. Graph line 114 shows the measured fault current if thecontacts 52 and 54 begin conducting at a voltage angle 90°, and showsthe current being symmetrical where the positive and negative peakvalues are at the same magnitude relative to zero. Thus, although thepeak-to-peak current is the same for symmetrical and asymmetricalcurrents, the absolute magnitude of the peaks is less for symmetricalcurrent, which reduces the stress on the electrical components in thenetwork 10 that are subjected to the fault current.

FIG. 5 is a graph with time on the horizontal axis and the position ofthe actuator housing 60 on the vertical axis, where graph line 120 showsthe position of the actuator housing 60 from when it starts moving toclose the contacts 52 and 54 until it returns to the contact openposition. The zero position is the position of the actuator housing 60where the movable core 92 is touching the E-shaped core 86, as shown inFIG. 3 . When the coil 88 is energized and the actuator housing 60 movesto close the contacts 52 and 54, initially compressing the springs 66 asthe movable contact 54 is moved towards the fixed contact 52, the gap 56will be reduced. When the position of the actuator housing 60 is atabout 5 mm shown by point 122 at about time 23 ms, the gap 56 is about 1mm, and conduction between the contacts 52 and 54 will begin across thegap 56, known as a pre-strike. As the actuator housing 60 continues tomove, the contacts 52 and 54 will engage at actuator position of about 4mm shown by point 124 at about time 24 ms, and the current to the coil88 will be shut off. The momentum of the actuator housing 60 willcontinue moving the actuator housing 60 until the position of theactuator housing 60 is about 1.5 mm at point 126 at about time 28 ms,shown as a gap 104 between the flanges 72 and 74 in FIG. 3 , when thecompression forces of the springs 66 and 78 are holding the contacts 52and 54 closed and the actuator housing 60 will reverse its direction. Atpoint 128, about time 32 ms, the contacts 52 and 54 will separate, butthere still is conduction across the gap 56 until the gap length isabout 3 mm, which occurs at point 130 at about time 35 ms. Onefundamental frequency cycle at 60 Hz is about 16.7 ms for 60 Hz, so thetime from the beginning of the conduction at time 23 ms until the end ofconduction at time 35 ms is 12 ms, which is about three-fourths of thecycle, where the current stops at the next zero current crossing. Thus,the current conduction time through the contacts 52 band 54 is onefundamental frequency cycle at 60 Hz. These times can be adjusted forsystems that operate at other frequencies.

The control of the switch assembly 50 as being described includesdriving the movable contact 54 into the fixed contact 52 and thenimmediately turning off the current applied to the coil 88, or reversingthe voltage on the coil 88 to drive the coil current to zero, so thatthe closing force between the contacts 52 and 54 is only provided by themomentum of the actuator 58 and the mass of the movable contact 54against the forces provided by the open spring 66 and the compliancespring 78, which bounces the movable contact 54 off of the fixed contact52. In other words, the velocity of the actuator 58 after the coil 88 isturned off, or otherwise has zero coil current, compresses thecompliance spring 78 until the stored energy in the moving mass of theactuator 58 and the movable contact 54 is transferred to the compliancespring 78, where the compliance spring 78 will push the contacts 52 and54 back open again. Thus, by intentionally bouncing the contacts 52 and54 for the low energy test in this manner, the potential fault currentduration is limited to one fundamental frequency current cycle asdescribed. Specifically, the control of the switch assembly 50 iscapable of opening the vacuum interrupter contacts 52 and 54 fast enoughto be able to interrupt current flow within 16.7 ms of the firstconduction between the contacts 52 and 54, which gives a totalconduction time from closing to opening the contacts 52 and 54 less than16.7 ms as measured from a 1 mm open pre-strike contact gap to a 3 mmopen contact gap. This results in one fundamental frequency currentcycle of symmetrical fault current, which is twice the time that thepresent single pulse would allow as known pulse testing a faultedcircuit results in a half-cycle of fault current. These times can beadjusted for systems that operate at other frequencies.

Thus, the switch assembly 50 is designed so that the moving mass of theactuator 58 and the movable contact 54, the size and length of thecompliance spring 78, the amount of current applied to the coil 88, thetime that the current is removed from the coil 88 during the closingoperation, etc. cause the contacts 52 and 54 to conduct for about onefundamental frequency cycle of fault current. Since the control of theswitch assembly 50 allows control of the position of the movable contact54 relative to time, the timing of the conduction between the contacts52 and 54 can be controlled so that current begins flowing at a 90°angle of the voltage waveform so that symmetrical currents flow insteadof asymmetrical currents when the contacts 52 and 54 are closed, whichreduces forces on the network components. Further, traditional vacuuminterrupters can be employed instead of more complex and specializedvacuum interrupters required for the known pulse testing.

Another embodiment includes closing the vacuum interrupter contacts 52and 54 at the voltage peak that drives transformers away fromsaturation, thereby keeping the transformers from saturating, where whena transformer is de-energized there is often a non-zero remnant flux inthe transformer core. Energization in-rush current results fromsaturation of the transformer core when it is energized at a voltagepoint where the new flux drives the transformer into saturation. Thiscan be reduced/eliminated by keeping a flux model of transformers insome form of memory, closing the vacuum interrupter contacts 52 and 54so that the flux will move toward zero rather than away from zero. Ifthe residual flux is the result of positive voltage the vacuuminterrupter contacts 52 and 54 close when the voltage is negative movingthe flux toward zero and minimizing the peak flux that drives thetransformer core into saturation. The flux at peak voltage is zerobecause it lags the voltage by 90°. If this is the case, thepoint-on-wave can be adjusted to correct the residual flux by closingslightly earlier than the peak of the voltage waveform.

Many of the examples used in this discussion were derived for powersystems operating at 60 Hz fundamental frequency. It is noted thatsimilar techniques can be applied to adjust the mechanism to operate atother fundamental frequencies.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present disclosure. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of thedisclosure as defined in the following claims.

What is claimed is:
 1. A method for operating a magnetically actuatedswitch assembly to perform a low energy test pulse, the switch assemblyincluding a fixed contact and a movable contact, the method comprising:energizing a magnetic actuator to move the moveable contact against thebias of at least one spring coupled to the movable contact towards thefixed contact to make contact therebetween, wherein AC current conductsacross a gap formed between the movable contact and the fixed contact asthe moveable contact is moved toward the fixed contact and before themovable contact and the fixed contact make contact; and reversing themagnetic actuator to move the movable contact away from the fixedcontract at least under the bias of the at least one spring so that theamount of time that the current conducts between the movable contact andthe fixed contact is about one fundamental frequency cycle of thecurrent, wherein reversing the magnetic actuator occurs at a time sothat when the movable contact and the fixed contact begin conducting anapplied voltage on the switch assembly is at or near a peak of thevoltage wave so that the current is symmetric.
 2. The method accordingto claim 1 wherein the at least one spring is a larger open spring and asmaller compliance spring.
 3. The method according to claim 2 whereinthe open spring is wrapped around a cylindrical housing and thecompliance spring is provided within the housing.
 4. The methodaccording to claim 3 wherein the magnetic actuator includes a stationarycore having a coil and a movable core that moves towards the stationarycore when the actuator is energized, and wherein reversing the magneticactuator comprises de-energizing the magnetic actuator or reversing anapplied voltage on the magnetic actuator.
 5. The method according toclaim 1 wherein the one fundamental frequency cycle of current is about16.7 ms for 60 Hz.
 6. The method according to claim 5 wherein the timethat the contacts begin conducting to the time the contacts willwithstand voltage when the current goes to zero is about three-quartersof the one fundamental frequency cycle time.
 7. The method according toclaim 1 wherein the voltage on the switch assembly that is at or nearthe peak of the voltage wave is at a 90° voltage angle.
 8. The methodaccording to claim 1 wherein the contacts are part of a vacuuminterrupter.
 9. The method according to claim 8 wherein the current is afault current in a medium voltage power distribution network and thevacuum interrupter is part of a recloser in the power distributionnetwork.
 10. A method for performing a reclosing fault testing operationin a power distribution network using a vacuum interrupter including afixed contact and a movable contact, the method comprising: energizing amagnetic actuator to move the movable contact against the bias of atleast one spring coupled to the movable contact towards the fixedcontact to make contact therebetween, wherein AC fault current conductsacross a gap formed between the movable contact and the fixed contact asthe moveable contact is moved toward the fixed contact and before themovable contact and the fixed contact make contact; and reversing themagnetic actuator to move the movable contact away from the fixedcontact at least under the assistance of the bias of the at least onespring so that the amount of time that the current conducts between themovable contact and the fixed contact is about one fundamental frequencycycle of the fault current.
 11. The method according to claim 10 whereinthe one fundamental frequency cycle of current is about 16.7 ms for 60Hz.
 12. The method according to claim 11 wherein the time that thecontacts begin conducting to the time the contacts will withstandvoltage when the current goes to zero is about three-quarters of the onefundamental frequency cycle time.
 13. The method according to claim 10wherein the at least one spring is a larger open spring and a smallercompliance spring.
 14. A magnetically actuated switch assembly having alow energy pulse test capability, the switch assembly comprising: afixed contact and a movable contact; a magnetic actuator coupled to themovable contact, the magnetic actuator configured, under a firstenergization, to move the moveable contact against the bias of at leastone spring coupled to the movable contact towards the fixed contact,wherein AC current conducts across a gap formed between the movablecontact and the fixed contact as the moveable contact is moved towardthe fixed contact and before the movable contact and the fixed contactmake contact; and the magnetic actuator, under a second energization,being further configured when the movable contact makes contact with thefixed contact to allow the bias of the at least one spring to move themovable contact away from the fixed contact so that the amount of timethat the current conducts between the movable contact and the fixedcontact is about one fundamental frequency cycle of the current, whereinsecond energization of the magnetic actuator occurs at a time so thatwhen the movable contact and the fixed contact begin conducting anapplied voltage on the switch assembly is at or near a peak of thevoltage wave so that the current is symmetric.
 15. The magneticallyactuated switch assembly according to claim 14 wherein the onefundamental frequency cycle of current is about 16.7 ms for 60 Hz. 16.The magnetically actuated switch assembly according to claim 15 whereinthe time that the contacts begin conducting to the time the contactswill withstand voltage when the current goes to zero is aboutthree-quarters of the one fundamental frequency cycle time.
 17. Themagnetically actuated switch assembly according to claim 14 wherein thevoltage on the switch assembly that is at or near the peak of thevoltage wave is at a 90° voltage angle.